Persist a generalized history of visited URL in history_file and try to keep it in sync during telescope usage and shutdown.

if telescope is started with an url while there is already another instance of it running and the -S flag is not provided, the link will be automagically opened into the running instance of telescope. Telescope now listens on a UNIX domain socket in ~/.telescope/ctl (or ~/.cache/telescope/ctl if XDG is used) for commands.

Telescope now remebers the last URL (per tab!) that replied with 1X (input request.) The new command reply-last-input allows to resend a query to that URL. It's particularly useful with capsules that make a heavy uses of 10 replies (search engines or similar, interactive pages, etc) because it both saves a network roundtrip and the user from looking for the "search" link all across the page ;-) idea from a conversation with thfr@, thanks!

I'd like to use parser{,_gophermap,_gemtext}.c in standalone testing programs, and this function is getting in the way since it depends on ui.c

Before we didn't save the scrolling position before a refresh (nohist=1) and that's annoying. This saves the scrolling position only in the correct case, which is when changing from a page to another, expect when switching to TAB_LAZY off.

load_url needs to know when a tab passes from lazy to not lazy to correctly saves the scrolling position (see follow-up commit.)

Save the offset to the first and current line of the buffers and restore it when the page is loaded. This restores almost the exact viewport: we save the offset of the *real* line in the document, but they get wrapped before being displayed, so the actual restored position may be slightly above from the original one (think of a long paragraph that gets wrapped over multiple visual lines.) In practice, this isn't a drawback but only an improvement over the current behaviour. In the future we could save also the offset *inside* the line, to restore the exact position, but that felt unnecessary for now. Persisting the postion on the session file ensures that even when re-opening telescope the scroll position is correct. There are some very active pages, such as antenna or other aggregator, where this feature doesn't really work well if you re-open the page after a while, since new links are available, but otherwise is a god sent! See also github issue #1

`url' may be a pointer to a string of the buffer which gets corrupted upon tab_stop. This bug shows when loadfn is load_about_url, because in make_fs_request we first tab_stop, and then send the request, which ends up sending to the fs process a free'd string. At least on OpenBSD with Otto' malloc is (partially) corrupted and will either make the fs process abort or return a not found page. One solution may be to rework make_fs_request to process things in a different order, but that would only hide the problem. Instead, use the newly created history element as url given to the loadfns: that is guaranteed to be valid up to the next load_url call. Reported by Brian Callahan, thanks!

it's not spelled `util.h' because otherwise it'd get included instead of /usr/include/util.h

- don't expose the evbuffer where we store the cached page - cache to/from tabs instead of buffers

the idiom if (load_next_page(...)) start_loading_anim(...); is fundamentally wrong because `load_next_page' (or previous page, or anything else that call into load_url) *may* load all the page before returning (thanks to the cache, but not only, cf. load_page_from_str.) Instead, let's call start_loadign_anim at the start of make_request so it's always called in the right moment. Cache and other special pages don't end up calling make_request anyway, and we already call stop_loading_anim when a request finishes (or fails.) move start_loading_anim up in make_request.